752 



THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1957 



The two-point load was chosen as a measure of the bending moment 

 for convenience in laboratory testing of new conduits. The two-point 

 load system is undoubtedly the simplest method for testing cylindrical 

 or near-cylindrical shapes in conventional compression testing machines 

 (crushing test). Since most of the supplementary conduit materials are 

 cylindrical in shape, the most obvious rec^uirement would be in terms 

 of minimum two-point loading. 



The data in Figs. 12, 13, and 14 were obtained as follows: 

 The bending moments at points perpendicular to the vertical axis 

 were represented, as a function of the applied load, by a straight line, 

 determined by the method of least scjuares. This was done for all the 

 investigated depths and backfill materials. The side points were used 

 as a basis of comparison because they were less affected by a change in 

 the bedding conditions. With reference to the considerations of the 







O 

 O 



o 



Q. 

 I 

 O 



t- 



H 

 Z 

 111 



_l 



> 

 O 



1300 

 1200 

 1100 

 1000 

 900 

 800 

 700 

 600 

 500 

 400 

 300 

 200 

 100 



a 



< 

 o 



Z 



a. 



backfill: fine sand 



WIDTH OF trench: I8-30IN. 

 CONDUIT MEAN D I A M ETE R : 4 IN. 



3000 LBS 

 BACKFILL ( LOOSE) 



X 



10 



_L 



20 30 40 



HEIGHT OF COVER (IN) 



50 



60 



Fig. 13 — Equivalent two-point load versus height of cover for sand backfill. 



